It is common practice in the art of hydroelectric power generation to provide a debris screening structure, commonly referred to as a trash rack, upstream of turbine intake conduits to stop large objects from entering into the conduits and potentially fouling or damaging the turbine machinery. Such trash racks are typically formed of a series of vertical or inclined, parallel pipes or bars anchored to the upstream face of a dam, or to the base of the dam, and extending to a height which may be above the headwater elevation. Objects and debris flowing with stream currents and pulled toward the intake conduits are stopped by the rack and retained upstream until physically removed by manual or mechanized rakes or other cleaning equipment.
A problem with conventional trash rack installations is their tendency to accumulate significant quantities of debris, ultimately resulting in operational problems associated with partial or complete trash rack failure (e.g., collapse) or significant head losses that negatively impact the productivity of the power generating facility. This negative impact is felt in terms of reduced power production, reduced operability, reduced availability and, consequently, in terms of lost revenue. For example, it is estimated that at one 5-turbine unit 175 MW river hydroelectric plant, trash rack losses of one foot of head represent an annual revenue loss of $500,000.00 at an energy value of $25.00 per MWh.
While various systems have been proposed for monitoring head losses across trash racks, these have not proven entirely satisfactory. For example, existing techniques do not accurately reflect real losses across the trash rack as flow rate through the rack changes, making loss data difficult to interpret. Moreover, known systems have not been integrated effectively in an overall control scheme designed to inform and alert operations personnel of the need to clean the trash rack, typically relying on spot checking or periodic cleaning schedules.
Another problem can arise in optimizing performance in a multi-unit hydro turbine plant. While a few systems are known for optimizing performance in multi-unit plants (e.g., distributing the loads among the turbine units to operate the plant as efficiently as possible or to generate a desired base load as efficiently as possible) including units of various capacities and efficiencies, the optimization systems heretofore all have based the analysis on assumed operating efficiencies of the turbine. However, when the various turbine units have unknown or differing amounts of trash build-up, the assumed operating efficiencies can no longer be assumed to apply. Thus, any optimization solution which fails to take this fact into account will not be an ideal distribution.
There is a need, therefore, for an improved system for monitoring fouling of trash racks in hydroelectric facilities, and for informing plant personnel or automated control systems of the real state of losses across the rack, both in terms of head loss and in terms of economic impact. There is also a need for an improved system for informing operations engineering and management personnel, or automated control systems, of the potential for trash rack failure due to excessive head losses. There is further a need for an improved multi-unit optimization method and system which accounts for varying amounts of trash build-up on the turbine units.